For a number of years, infusers have been used that provide the patient or user with the means for administering a drug in an easy way without requiring a medically trained person, such as a physician or a nurse, to handle the device.
In order to reduce the size of the infuser, a number of alternative designs regarding the plunger rod have been developed, in particular since the plunger rod conventionally is an elongated rod having a length that enables it to empty a tubular medicament container. Document EP 1 326 659 discloses an injecting device having a flexible plunger rod bendable around a guiding wheel. The plunger rod is driven by an electric motor, via a transmission, to empty a medicament container. The drawback with the solution according to EP 1 326 659 is that the guiding wheel is rather large and is positioned behind the medicament container, as seen in a longitudinal direction, making the device unnecessary long.
Document WO 2010/112377 discloses a reusable medicament delivery device. In order to reduce the length of the device, the plunger rod is arranged in two telescopically arranged parts. The telescopic action requires two compression springs, rendering the device rather long. The device is further arranged with an electric motor. The motor, operably connected to an elongate member, is arranged to control the dose delivery movement of the plunger rods. Further, the motor is also used for retracting the plunger rods after completed dose delivery in order to be able to replace the medicament container.
Another drawback with many of the mentioned devices is that there is no feature or mechanism for handling the injection needle, neither automatic penetration nor automatic withdrawal.
WO 2013/153041 discloses an infusion device having a purely mechanical drive mechanism, including a mechanism for penetration and later withdrawal of the injection needle. Even though the device has proven advantages, especially the modular plunger rod and the injection speed control, it contains a large number of components that need to interact with each other in order to create the desired functionality.
In view of the above, there is still room for improvements regarding this type of medicament delivery device.